Thermoplastic aromatic polyester resins, polyolefin resins and polyamide resins each are well known engineering plastics which exhibit excellent moldability characteristics. Furthermore, these resins exhibit desirable mechanical properties, electrical properties and the like which make them suitable materials for a wide range of end-use applications. Specifically, aromatic polyesters and polyamide resin are known to possess excellent chemical resistance characteristics. While such resins have property characteristics which are desirable, there is still a need for property improvements and/or enhancements, particularly where new end-use applications are identified which require specialized properties.
For example, aromatic polyester resins are frequently required to exhibit greater toughness, impact-resistance, heat-resistance and alkali-resistance properties. Polyamide resins are typically required to have improved water absorption resistance characteristics and increased dimensional stability. Olefins resins such as polyethylene and polypropylene, on the other hand, generally are relatively light-weight, and possess excellent chemical resistance and flexibility characteristics. Olefin resins, however, typically lack strength and rigidity which sometimes precludes their use in certain end-use applications where strength and rigidity are requisite attributes of the engineering plastic.
Aromatic polyester and polyolefin resins have relatively poor affinity for one another. Thus, when such resins are formed as distinct layers or regions in a composite article (such as a co-extruded laminated film structure having respective layers of an aromatic polyester and a polyolefin), there is a tendency for the composite article to delaminate along the boundary region between the aromatic polyester layer and the polyolefin resin layer due to poor adherence characteristics.
Generally, blending of resins so as to achieve a desirable set of property attributes has typically been thought to be useful for solving or reducing the problems associated with any one individual resin. For example, the homogenous blending of an aromatic polyester resin and a polyolefin resin would be expected to compensate for the drawbacks associated with the respective resins so as to achieve a composition having improved fusability and bondability. However, the compatibility of aromatic resins and polyolefin resins is so poor that even when melt-blended with one another, it is difficult to obtain a homogenous dispersion. In particular, when injection molded articles are formed from a blend of an aromatic polyester and a polyolefin, severe surface peeling occurs due to an inhomogeneous blend. The resulting mechanical properties of such a blend are also significantly lower than what might otherwise be expected. These problems, therefore, tend to limit the practical value of such a resin blend.
Various proposals have been made in order to obtain a homogenous dispersion of an aromatic polyester resin and a polyolefin resin by improving their compatibility characteristics. In this regard, it has been proposed that a modified polyolefin copolymer be employed which contains comonomeric units introduced into the polymer's backbone for the purpose of enhancing the compatibility between the polyester and polyolefin resins. Although such a "compatibilizing agent" does improve the compatibility of polyester and polyolefin resins to some extent, further improvements in terms of dispersibility and mechanical properties are needed.
Blending of an aromatic polyester resin and a polyamide resin is considered useful in order to improve not only the heat-resistance properties of the aromatic resin, but also to improve the water absorption resistance properties of the polyamide resin. It might be expected, therefore, that a composition which contains both an aromatic polyester resin and a polyamide resin would benefit from the advantageous properties, such as mechanical strength and the like, attributable to each of the resin components. The present applicants, however, have determined that the compatibility of aromatic polyester and polyamide resins is so poor that, when simply melt-blended with one another, it is difficult to obtain a homogeneous dispersion, which results in substantially lower mechanical strength properties than would otherwise be expected. Like the aromatic polyester and olefin blend discussed above, an inhomogeneous blend of an aromatic polyester and a polyamide will result in significant surface peeling on injection-molded articles. As a result, the practical value of such a blend is questionable.
What has been needed therefore is a better compatibilization technique to enable aromatic polyesters to be blended sufficiently with either a polyolefin or a polyamide resin. It is towards fulfiling such a need that the present invention is directed.
Broadly, the present invention is embodied in moldable polyester resin compositions which contain a modified aromatic polyester copolymer having metal-sulfonate-containing units introduced into the copolymer's backbone structure. Such an aromatic polyester copolymer has been found to be highly compatible with both polyolefin and polyamide resins, and serves as a compatibilizer when an unmodified (i.e., one not containing metal-sulfonate units) aromatic polyester is further blended with the modified polyester copolymer and either a polyolefin or a polyamide resin.
Preferred embodiments of this invention will include, based on the total weight of the resin components:
(A) between 2 to 98% by weight of a modified aromatic polyester copolymer containing a metal sulfonate group which is the polycondensation reaction product of (a) an aromatic dicarboxylic acid or its ester-forming derivative, (b) a diol compound or its ester-forming derivative, and (c) an ester-forming compound containing a metal sulfonate group;
(B) between 2 to 98% by weight of one of (B-I) an olefin copolymer produced by copolymerizing an olefin with at least one of an .alpha.,.beta.-unsaturated carboxylic acid or its derivative and a vinyl alcohol or its ester, and (B-II) a polyamide resin; and, optionally
(C) between 0 to 96% by weight of an unmodified aromatic polyester resin.
By the term "modified aromatic polyester" is meant to refer to an aromatic polyester copolymer having metal-sulfonate-containing units as part of its backbone. On the other hand, by the term "unmodified aromatic polyester" is meant to refer to aromatic polyesters which do not include such metal-sulfonate-containing units as part of their backbone structures.
Further aspects and advantages of this invention will become more clear after careful consideration is given to the detailed description of the preferred exemplary embodiments which follow.